refactor app command sync and other fixes

[onerandomusername]

Summary

Refactors app command sync and lays the groundwork to implement GH-665 (but doesn't do it as of now)

• closes GH-260
• closes GH-265
• closes GH-277
• closes GH-433
• closes GH-468
• closes GH-631

Checklist

I have not extensively tested or caught most cases, but a review (even in this condition) would be appreciated

• [ ] If code changes were made, then they have been tested
  • [ ] I have updated the documentation to reflect the changes
  • [x] I have formatted the code properly by running task lint
  • [x] I have type-checked the code by running task pyright
• [ ] This PR fixes an issue
• [ ] This PR adds something new (e.g. new method or parameters)
• [x] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] This PR is not a code change (e.g. documentation, README, ...)

[shiftinv]

Not sure what happened here, merging #667 resulted in GitHub automatically closing this PR, instead of changing the base branch to master like it should've:

If you delete a head branch after its pull request has been merged, GitHub checks for any open pull requests in the same repository that specify the deleted branch as their base branch. GitHub automatically updates any such pull requests, changing their base branch to the merged pull request's base branch.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/about-branches#working-with-branches

This worked fine in #616 - in any case, GitHub doesn't allow reopening this PR, looks like you may have to recreate it, sorry :/ (Perhaps due to different source repos? The documentation doesn't appear to mention anything about that though.)

[shiftinv]

... should be fixed except for merge conflicts, thanks to https://github.com/github/docs/discussions/18311.

[shiftinv]

@onerandomusername Could you resolve the conflicts in this PR?

[onerandomusername]

This isn't ready yet.

[onerandomusername]

@onerandomusername would you please resolve conflicts?

[onerandomusername]

@onerandomusername would you please resolve conflicts?

done

[shiftinv]

Since this has become somewhat outdated, and given the number of merge conflicts that have cropped up, I believe this can be closed in favour of #1107 - nonetheless, thanks for the work on this PR c: